Based on data collected by governments and analysts from around the world, the research center estimated North Korea's arsenal at 20-30 warheads, up from 10-20 warheads at the same time last year.
The findings, released on Tuesday, come a year after the June 12, 2018, summit between President Donald Trump and North Korean leader Kim Jong Un in Singapore, which produced an agreement stating that North Korea would work towards "complete denuclearization of the Korean Peninsula."
But while Kim promised to dismantle missile facilities in the presence of international inspectors and offered to take steps such as shutting down the country's main Yongbyon nuclear complex in exchange for concessions, little progress has been made.
A second summit held in Hanoi, Vietnam, ended abruptly without any further agreements and since then, negotiations between the United States and North Korea have been at an impasse.
Almost immediately after the Hanoi summit, North Korea began restoring a missile test site that it had partially dismantled months before, and it has shown no signs of slowing down its weapons program.
Commercial satellite data shows that uranium enrichment operations are ongoing at the Yongbyon site, according to North Korea analysis website 38 North.
North Korea also resumed missile launches last month for the first time since late 2017. A report released by the U.S. Congressional Research Service last week concluded that the three projectiles fired on May 4 and May 9 were short-range ballistic missiles.
Pyongyang has ratcheted up the rhetorical heat recently, with a foreign ministry spokesman saying last week that "there is a limit to our patience" regarding negotiations with Washington.
In an April speech, Kim set a time limit for revisiting talks, saying Washington should come up "with a proper method of calculation before the end of this year."
Trump on Tuesday painted a sunnier picture of relations with North Korea. He told reporters that he had received a "beautiful" and "very warm" letter from Kim and said that he believed "something will happen that's going to be very positive."
South Korean President Moon Jae-in also shared an optimistic view of the North Korean peace process at a forum in Oslo, Norway, on Wednesday, saying that the stalemate in negotiations was "because we need some time to understand each other thoroughly."
"What we need now is not a new vision or proclamation," he said, "but the deepening of mutual understanding and trust."
The Research Center for Nuclear Weapons Abolition estimates the entire global inventory of nuclear warheads now stands at 13,880, a decrease of 570 from a year ago.
Russia maintains the largest stockpile of warheads, with 6,500, while the United States follows closely with 6,185. The other countries possessing nuclear weapons are France, China, the United Kingdom, Israel, Pakistan, India and North Korea.